BERLIN (Reuters) - Talks between the European Union and United States on a transatlantic trade accord will stretch into 2016, the EU’s chief negotiator said on Tuesday, adding that the discussions were about to enter a “more difficult” and “intense” stage.

This year is seen as crucial in making progress on the Transatlantic Trade and Investment Partnership (TTIP), with the U.S. presidential election set for 2016 and President Barack Obama leaving office in January 2017.

Nothing has been agreed so far and expectations of a rapid deal are low.

“At this point in time I don’t want to rule in or rule out anything in terms of what is possible before the end of this year,” the EU’s chief negotiator Ignacio Garcia Bercero told a news conference in Berlin.

“But it is clear that a completion of the negotiations, a conclusion of the agreement, that is something that will require more time than 2015,” he said, adding that he did not believe the forthcoming U.S. election campaign would derail the talks.

“The United States has been telling us very clearly that they can continue negotiating with us in 2016.”

Obama has called for trade talks with Europe to make major progress this year following an agreement on trade promotion authority in Congress.

One of the major stumbling blocks for the deal, which seeks to reduce trade barriers and harmonize regulations, is an investor protection clause wanted by the Americans.

Many in Europe fear U.S. multinationals will use a so-called investor-to-state dispute settlement (ISDS) mechanism to challenge Europe’s food, labor and environmental laws on the grounds that these restrict free commerce.

Talks on ISDS have been suspended since last year. But Bercero signaled the EU Commission was gearing up to set out its suggestion on how the mechanism could be reformed.

Proponents of a deal say it could add $100 billion in annual economic output on both sides of the Atlantic, but the pact has also faced opposition, with thousands of people marching through German cities earlier this month to protest against the talks.